NEW DELHI — Poonam Devi moans in pain on the stretcher in the packed hospital emergency room, her ankles and wrists swollen, an IV hooked up to left arm to hydrate her. Patients like her, fevered, aching, unable to walk or sit on their own, are packing hospitals across New Delhi because of chikungunya, a mosquito-borne viral illness. The cycle of illness and packed hospital “fever clinics” plays out every year as monsoon rains fill puddles and open drains in the teeming city, creating swarms of mosquitoes that thrive in the warm, damp weather. The epidemics start promptly in August and stay for months, sickening tens of thousands and killing dozens, each year seeming to catch the government and population unprepared for it.